Send all incoming traffic on an interface to a listening port (iptables)
Send all incoming TCP traffic on interface eth1 to port 3128 on any interface:
sudo iptables -A PREROUTING -i eth1 -p tcp -j REDIRECT --to-ports 3128
iptables output should look like:
# iptables -t nat -nvL PREROUTING
Chain PREROUTING (policy ACCEPT 516K packets, 51M bytes)
pkts bytes target prot opt in out source destination
....
xxxK xxxM REDIRECT tcp -- eth1 * 0.0.0.0/0 0.0.0.0/0 redir ports 3128